"Va dans ton lit."
This literally translates to "Go in your bed".
Here are some other ways to say it, depending on the context:
* "Entre dans ton lit." (Enter your bed)
* "Couche-toi." (Go to bed/Lie down) - This is a more general phrase for going to bed, not specifically entering the bed.
* "Mettez-vous au lit." (Get into bed) - This is more formal.
The best option will depend on the situation and your relationship with the person you are speaking to.